Singlet oxygen and peroxyl radical (in lipid compartments)

Singlet oxygen (^1O2) and lipid peroxyl radicals (LOO•) are transient, highly reactive oxygen species that are major initiators and propagators of *lipid peroxidation* in biological membranes. Singlet oxygen is typically formed by photodynamic action, enzymatic reactions, or decomposition of lipid hydroperoxides, while peroxyl radicals arise from the reaction of lipid radicals with molecular oxygen[1][2][3][4][5]. In lipid compartments, especially those enriched in polyunsaturated fatty acids, these species trigger and propagate oxidative chain reactions that compromise membrane integrity, alter signal transduction, and can drive forms of regulated cell death (e.g., ferroptosis, necrosis)[3][7]. This lipid peroxidation process is implicated in the pathogenesis of multiple diseases, including cancer, inflammation, neurodegenerative and cardiovascular diseases[3][5]. Markers of their activity include malondialdehyde, protein carbonyls, and specific cholesterol oxidation products[2][4]. Antioxidants and iron chelators can attenuate their harmful effects, whereas photosensitizing drugs deliberately increase singlet oxygen production, for example in photodynamic therapy[1][4][7]. They are thus not "targets" per se, but represent central intermediates whose modulation is critical to oxidative damage or therapy in lipid-rich cellular environments.

Other names

^1O2 (singlet oxygen)LOO• (lipid peroxyl radical)ROO• (peroxyl radical)reactive oxygen species in lipids

Antioxidants donate electrons or hydrogen atoms to neutralize peroxyl radicals and prevent propagation[5]. Photosensitizers absorb light and transfer energy to molecular oxygen to generate singlet oxygen[1][4].